Nuclear power plant and a method of conditioning its power generation circuit

ABSTRACT

In a nuclear power plant making use of a high temperature gas cooled reactor, it is necessary, prior to commencing power generation and connection of a generator to an electrical distribution grid, to condition the power generation circuit of the plant. This involves creating stable conditions within the power generation circuit. To this end, the plant includes a start-up blower system for circulating working fluid, typically helium, around the power generation circuit until the desired conditions are satisfied. The start-up blower system typically includes a normally open in-line valve, at least one blower connected in parallel with the in-line valve and a normally closed isolation valve connected in series with the blower. Conditioning the power generation circuit will typically include stabilizing the pressure in the circuit at between 10 bar and 50 bar.

[0001] THIS INVENTION relates to a nuclear power plant. It also relatesto a method of conditioning the power generation circuit of a nuclearpower plant.

[0002] According to one aspect of the invention there is provided anuclear power plant which includes

[0003] a closed loop power generation circuit making use of gas as aworking fluid; and

[0004] a start-up blower system for conditioning the power generationcircuit.

[0005] Typically the working fluid is helium.

[0006] The power generation circuit may include a nuclear reactor havinga working fluid inlet and a working fluid outlet, a turbine arrangement,an upstream side of which is connected to the outlet of the reactor, atleast one compressor and at least one heat exchanger, the plant furtherincluding

[0007] a generator to which the turbine arrangement is drivinglyconnected; and

[0008] a variable resistor bank which is disconnectably connectable tothe generator.

[0009] The turbine arrangement may include a high pressure turbinedrivingly connected to a high pressure compressor, a low pressureturbine drivingly connected to a low pressure compressor and a powerturbine drivingly connected to the generator.

[0010] The power generation circuit may includes a recuperator which hasa high pressure side and a low pressure side, each side of therecuperator having an inlet and an outlet, a pre-cooler connectedbetween an outlet of the low pressure side of the recuperator and aninlet of the low pressure compressor and an inter-cooler connectedbetween an outlet of the low pressure compressor and an inlet of thehigh pressure compressor, the start-up blower system being positionedbetween the outlet of the low pressure side of the recuperator and aninlet of the pre-cooler.

[0011] The power generation circuit may include a low pressurerecirculation line in which a low pressure recirculation valve ismounted, the low pressure recirculation line extending from a positionbetween the outlet of the low pressure compressor and an inlet of theinter-cooler to a position between the start-up blower system and theinlet of the pre-cooler.

[0012] The power generation circuit may include a high pressurerecirculation line in which a high pressure recirculation valve ismounted, the line extending from a position between an outlet of thehigh pressure compressor and the inlet of the high pressure side of therecuperator to a position between the outlet of the low pressurecompressor and an inlet of the inter-cooler.

[0013] The power generation circuit may include a recuperator bypassline in which a recuperator bypass valve is mounted, the bypass lineextending from a position upstream of the inlet of the high pressureside of the recuperator to a position downstream of the outlet of thehigh pressure side of the recuperator.

[0014] The power generation circuit may further include a high pressurecoolant valve and a low pressure coolant valve, the high pressurecoolant valve being configured, when open, to provide a bypass of heliumfrom the high pressure side of the high pressure compressor to the inletof the low pressure turbine, the low pressure coolant valve beingconfigured to provide a bypass of helium from the high pressure side ofthe high pressure compressor to the inlet of the power turbine.

[0015] The start-up blower system may include, in parallel, a start-upblower and a normally open start-up blower system in-line valve whichvalve is connected in series between the low pressure side of therecuperator and the pre-cooler.

[0016] Preferably the start-up blower system includes two blowersconnected in parallel and a normally closed isolation valve associatedwith each blower.

[0017] The nuclear reactor may be a high temperature helium cooledpebble bed reactor making use of spherical fuel elements.

[0018] To bring the nuclear power plant into a standby mode ready forpower operation and connection to the grid, stable conditions must becreated in the power generation circuit, this is referred to asconditioning of the power generation circuit.

[0019] According to another aspect of the invention, in a nuclear powerplant which includes a closed loop power generation circuit there isprovided a method of conditioning the power generation circuit whichinclude the step of circulating helium around the power generationcircuit by means of a start-up blower system.

[0020] The start-up blower system may have a normally open start-upblower system in-line valve, at least one blower connected in parallelwith the start-up blower system in-line valve and a normally closedisolation valve connected in series with the or each blower, and themethod may include the steps of

[0021] closing the start-up blower system in-line valve;

[0022] opening the or each isolation valve; and

[0023] operating the or each blower to circulate helium around the powergeneration circuit.

[0024] The method may include stabilizing the pressure in the powergeneration circuit at a pressure between 10 bar and 50 bar.

[0025] When the plant is configured, during normal operation, to use aBrayton cycle as the thermodynamic conversion cycle, and the powergeneration circuit includes a high pressure compressor, a low pressurecompressor, a high pressure recirculation line, whereby helium can berecirculated around the high pressure compressor, a low pressurerecirculation line whereby helium can be recirculated around the lowpressure compressor and a high pressure recirculation valve and a lowpressure recirculation valve for regulating the flow of helium throughthe high pressure recirculation line and low pressure recirculationline, respectively, in order to prevent premature starting of theBrayton cycle, the method may include the step of opening at least oneand preferably both of the high and low pressure recirculation valves.

[0026] The method may include regulating the temperature of gas enteringthe start-up blower system thereby to reduce the risk of damage to thestart-up blower system.

[0027] The method may include restricting the outlet temperature of thestart-up blower system to a temperature below a predetermined value,typically a temperature of not greater than 250° C.

[0028] When the power generation circuit includes a recuperator having ahigh pressure side and a low pressure side, the method may include thestep of regulating the temperature of the helium entering therecuperator.

[0029] The method may include limiting the temperature of heliumentering the recuperator to a temperature not higher than 600° C.

[0030] When the plant includes a recuperator by-pass line configured topermit helium to by-pass the high pressure side of the recuperator and arecuperator by-pass valve for regulating the flow of helium through therecuperator by-pass line, regulating the temperature of helium enteringthe recuperator may include operating the recuperator by-pass valve toregulate the flow of helium through the recuperator.

[0031] When the power generation circuit includes a high pressurecoolant valve and a low pressure coolant valve which are configured,when opened, to provide a by-pass of helium from the high pressure sideof the high pressure compressor to the inlet of the low pressure turbineand from the high pressure side of the high pressure compressor to theinlet of the power turbine, regulating the temperature of heliumentering the recuperator may include operating at least one of the highpressure coolant valve and the low pressure coolant valve.

[0032] The method may include operating the recuperator bypass valve inorder to regulate the reactor inlet temperature and control thetemperature of the start-up blower system. Operating the recuperatorbypass valve enables also the coolers in the system to remove the heatgenerated in the core more effectively. Preferably, the recuperatorbypass valve is operated to keep the outlet temperature of the start-upblower system below a predetermined value, typically 250° C.

[0033] When the plant includes a power turbine drivingly connected to agenerator the method may include the step of stabilizing and controllingthe speed of the power turbine.

[0034] Stabilizing and controlling the speed of the power turbine may beachieved by varying the load on the generator.

[0035] The method may include varying the electrical load on thegenerator by means of a variable resistor bank.

[0036] The invention will now be described, by way of example, withreference to the accompanying diagrammatic drawing which shows aschematic representation of a nuclear power plant in accordance with theinvention.

[0037] In the drawing, reference numeral 10 refers generally to part ofa nuclear power plant in accordance with the invention.

[0038] The nuclear power plant 10 includes a closed loop powergeneration circuit, generally indicated by reference numeral 12. Thepower generation circuit 12 includes a nuclear reactor 14, a highpressure turbine 16, a low pressure turbine 18, a power turbine 20, arecuperator 22, a pre-cooler 24, a low pressure compressor 26, aninter-cooler 28 and a high pressure compressor 30.

[0039] The reactor 14 is a pebble bed reactor making use of sphericalfuel elements. The reactor 14 has a helium inlet 14.1 and a heliumoutlet 14.2.

[0040] The high pressure turbine 16 is drivingly connected to the highpressure compressor 30 and has an upstream side or inlet 16.1 and adownstream side or outlet 16.2, the inlet 16.1 being connected to theoutlet 14.2 of the reactor 14.

[0041] The low pressure turbine 18 is drivingly connected to the lowpressure compressor 26 and has an upstream side or inlet 18.1 and adownstream side or outlet 18.2. The inlet 18.1 is connected to theoutlet 16.2 of the high pressure turbine 16.

[0042] The nuclear power plant 10 includes a generator, generallyindicated by reference numeral 32 to which the power turbine 20 isdrivingly connected. The power turbine 20 includes an upstream side orinlet 20.1 and a downstream side or outlet 20.2. The inlet 20.1 of thepower turbine 20 is connected to the outlet 18.2 of the low pressureturbine 18.

[0043] A variable resistor bank 33 is disconnectably connectable to thegenerator 32.

[0044] The recuperator 22 has a hot or low pressure side 34 and a coldor high pressure side 36. The low pressure side of the recuperator 34has an inlet 34.1 and an outlet 34.2. The inlet 34.1 of the low pressureside is connected to the outlet 20.2 of the power turbine 20.

[0045] The pre-cooler 24 is a helium to water heat exchanger andincludes a helium inlet 24.1 and a helium outlet 24.2. The inlet 24.1 ofthe pre-cooler 24 is connected to the outlet 34.2 of the low pressureside 34 of the recuperator 22.

[0046] The low pressure compressor 26 has an upstream side or inlet 26.1and a downstream side or outlet 26.2. The inlet 26.1 of the low pressurecompressor 26 is connected to the helium outlet 24.2 of the pre-cooler24.

[0047] The inter-cooler 28 is a helium to water heat exchanger andincludes a helium inlet 28.1 and a helium outlet 28.2. The helium inlet28.1 is connected to the outlet 26.2 of the low pressure compressor 26.

[0048] The high pressure compressor 30 includes an upstream side orinlet 30.1 and a downstream side or outlet 30.2. The inlet 30.1 of thehigh pressure compressor 30 is connected to the helium outlet 28.2 ofthe inter-cooler 28. The outlet 30.2 of the high pressure compressor 30is connected to an inlet 36.1 of the high pressure side of therecuperator 22. An outlet 36.2 of the high pressure side of therecuperator 22 is connected to the inlet 14.1 of the reactor 14.

[0049] The nuclear power plant 10 includes a start-up blower systemgenerally indicated by reference numeral 38 connected between the outlet34.2 of the low pressure side 34 of the recuperator 22 and the inlet24.1 of the pre-cooler 24.

[0050] The start-up blower system 38 includes a normally open start-upblower system in-line valve 40 which is connected in-line between theoutlet 34.2 of the low pressure side of the recuperator and the inlet24.1 of the pre-cooler 24. Two blowers 42 are connected in parallel withthe start-up blower system in-line valve 40 and a normally closedisolation valve 44 is associated with and connected in series with eachblower 42.

[0051] A low pressure compressor recirculation line 46 extends from aposition between the outlet or downstream side 26.2 of the low pressurecompressor 26 and the inlet 28.1 of the inter-cooler 28 to a positionbetween the start-up blower system 38 and the inlet 24.1 of thepre-cooler 24. A normally closed low pressure recirculation valve 48 ismounted in the low pressure compressor recirculation line 46.

[0052] A high pressure compressor recirculation line 50 extends from aposition between the outlet or downstream side 30.2 of the high pressurecompressor and the inlet 36.1 of the high pressure side 36 of therecuperator 22 to a position between the outlet or downstream side 26.2of the low pressure compressor 26 and the inlet 28.1 of the inter-cooler28. A normally closed high pressure recirculation valve 51 is mounted inthe high pressure compressor recirculation line 50.

[0053] A recuperator bypass line 52 extends from a position upstream ofthe inlet 36.1 of the high pressure side 36 of the recuperator 22 to aposition downstream of the outlet 36.2 of the high pressure side 36 ofthe recuperator 22. A normally closed recuperator bypass valve 54 ismounted in the recuperator bypass line 52.

[0054] The plant 10 includes a high pressure coolant valve 56 and a lowpressure coolant valve 58. The high pressure coolant valve 56 isconfigured, when open, to provide a bypass of helium from the highpressure side or outlet 30.2 of the high pressure compressor 30 to theinlet or low pressure side 18.1 of the low pressure turbine 18. The lowpressure coolant valve 58 is configured, when open, to provide a bypassof helium from the high pressure side or outlet 30.2 of the highpressure compressor 30 to the inlet 20.1 of the power turbine 20.

[0055] To bring the nuclear power plant 10 from a standby mode to apower operation mode, stable thermodynamic conditions should be createdin the power generation circuit 12. This is referred to as conditioningof the power generation circuit for power operation.

[0056] In use, in order to condition the power generation circuit forthe power operation mode, the procedure to start the start-up blowersystem is executed. More particularly, the start-up blower in-line valve40 is closed. Each of the isolation valves 44 is opened and the blowers42 are operated to stabilise the mass flow in the power generationcircuit.

[0057] The power generation circuit 12 is configured to make use of aBrayton cycle as the thermodynamic conversion cycle and in order toprevent premature starting of the Brayton cycle, the high and lowpressure compressor recirculation valves 48, 51 are opened.

[0058] The position of the recuperator bypass valve 54 and the speed ofthe blowers 42 are controlled to regulate the conditioning temperaturein the reactor.

[0059] In order to reduce the risk of damage to the blowers 42 it isimportant that the maximum temperatures in the blowers be maintainedbelow a predetermined maximum temperature, typically 250° C. In thisregard, the recuperator bypass valve 54 is operated which controls thecore inlet temperature and so indirectly the maximum temperature in thestart-up blower system 38.

[0060] Further, in order to regulate the maximum temperature in therecuperator 22, one or both of the high pressure coolant bypass valve 56and low pressure coolant bypass valve 58 are operated in order to ensurethat the maximum temperature in the recuperator remains below apredetermined maximum temperature, typically 600° C.

[0061] When stable conditions are achieved in the power generationcircuit 12, the nuclear power plant 10 is in power operation mode, readyfor power production and connection to the grid.

1. A nuclear power plant which includes a closed loop power generationcircuit making use of gas as a working fluid, the power generationcircuit including a nuclear reactor having a working fluid inlet and aworking fluid outlet, a high pressure turbine drivingly connected to ahigh pressure compressor, a low pressure turbine drivingly connected toa low pressure compressor and a power turbine drivingly connected to agenerator, a recuperator which has a high pressure side and a lowpressure side, each side of the recuperator having an inlet and anoutlet, a pre-cooler connected between an outlet of the low pressureside of the recuperator and an inlet of the high pressure compressor,and an intercooler connected between the outlet of the low pressurecompressor and an inlet of the high pressure compressor; and a start-upblower system for conditioning the power generation circuit, thestart-up blower system being positioned between the outlet of the lowpressure side of the recuperator and an inlet of the pre-cooler. 2.(Cancelled).
 3. (Cancelled).
 4. (Cancelled).
 5. A plant as claimed inclaim 1, in which the power generation circuit includes a low pressurerecirculation line in which a low pressure recirculation valve ismounted, the low pressure recirculation line extending from a positionbetween the outlet of the low pressure compressor and an inlet of theinter-cooler to a position between the start-up blower system and theinlet of the pre-cooler and a high pressure recirculation line in whicha high pressure recirculation valve is mounted, the line extending froma position between an outlet of the high pressure compressor and theinlet of the high pressure side of the recuperator to a position betweenthe outlet of the low pressure compressor and an inlet of theinter-cooler.
 6. (Cancelled).
 7. A plant as claimed in claim 5, in whichthe power generation circuit includes a recuperator bypass line in whicha recuperator bypass valve is mounted, the bypass line extending from aposition upstream of the inlet of the high pressure side of therecuperator to a position downstream of the outlet of the high pressureside of the recuperator.
 8. A plant as claimed in claim 5, in which thepower generation circuit further includes a high pressure coolant valveand a low pressure coolant valve, the high pressure coolant valve beingconfigured, when open, to provide a bypass of helium from the highpressure side of the high pressure compressor to the inlet of the lowpressure turbine, the low pressure coolant valve being configured toprovide a bypass of helium from the high pressure side of the highpressure compressor to the inlet of the power turbine.
 9. A plant asclaimed in claim 5, in which the start-up blower system includes, inparallel, a start-up blower and a normally open start-up blower systemin-line valve which valve is connected in series between the lowpressure side of the recuperator and the pre-cooler.
 10. A plant asclaimed in claim 9, in which the start-up blower system includes twoblowers connected in parallel and a normally closed isolation valveassociated with each blower.
 11. A plant as claimed in claim 1, in whichthe nuclear reactor is a high temperature helium cooled pebble bedreactor making use of spherical fuel elements.
 12. (Cancelled). 13.(Cancelled).
 14. (Cancelled).
 15. In a nuclear power plant which isconfigured to use a Brayton cycle as the thermodynamic conversion cycleand which includes a closed loop power generation circuit including ahigh pressure compressor, a low pressure compressor, a high pressurerecirculation line, whereby helium can be recirculated around the highpressure compressor, a low pressure recirculation line whereby heliumcan be recirculated around the low pressure compressor and a highpressure recirculation valve and a low pressure recirculation valve forregulating the flow of helium through the high pressure recirculationline and low pressure recirculation line, respectively, there isprovided a method of conditioning the power generation circuit whichincludes the step of circulating helium around the power generationcircuit by means of a start-up blower system and opening at least one ofthe high and low pressure recirculation valves in order to preventpremature starting of the Brayton cycle.
 16. A method as claimed inclaim 15, which includes regulating the temperature of gas entering thestart-up blower system.
 17. A method as claimed in claim 16, whichincludes restricting the outlet temperature of the start-up blowersystem to a temperature of not greater than 250° C.
 18. A method asclaimed in claim 17, which, when the power generation circuit includes arecuperator having a high pressure side and a low pressure side,includes the step of regulating the temperature of the helium enteringthe recuperator.
 19. A method as claimed in claim 18, which includeslimiting the temperature of helium entering the recuperator to atemperature not higher than 600° C.
 20. A method as claimed in claim 18,in which, where the plant includes a recuperator by-pass line configuredto permit helium to by-pass the high pressure side of the recuperatorand a recuperator by-pass valve for regulating the flow of heliumthrough the recuperator by-pass line, regulating the temperature ofhelium entering the recuperator includes operating the recuperatorby-pass valve to regulate the flow of helium through the recuperator.21. A method as claimed in claim 18, in which, when the power generationcircuit includes a high pressure coolant valve and a low pressurecoolant valve which are configured, when opened, to provide a by-pass ofhelium from the high pressure side of the high pressure compressor tothe inlet of the low pressure turbine and from the high pressure side ofthe high pressure compressor to the inlet of the power turbine,respectively, regulating the temperature of helium entering therecuperator includes operating at least one of the high pressure coolantvalve and the low pressure coolant valve.
 22. A method as claimed inclaim 21, which, when the plant includes a power turbine drivinglyconnected to a generator, includes the step of stabilizing andcontrolling the speed of the power turbine.
 23. A method as claimed inclaim 22, in which stabilizing and controlling the speed of the powerturbine is achieved by varying the load on the generator.
 24. A methodas claimed in claim 23, which includes varying the electrical load onthe generator by means of a variable resistor bank.
 25. (Cancelled). 26.(Cancelled).
 27. (Cancelled).
 28. A plant as claimed in claim 1, inwhich the start-up blower system has a normally open start-up blowersystem in-line valve, at least one blower connected in parallel with thestart-up blower system in-line valve and a normally closed isolationvalve connected in series with the or each blower.
 29. A plant asclaimed in claim 1, which includes a variable resistor bank which isdisconnectably connectable to the generator.
 30. A method as claimed inclaim 15, which, when the start-up blower system has a normally openstart-up blower system in-line valve, at least one blower connected inparallel with the start-up blower system in-line valve and a normallyclosed isolation valve connected in series with the or each blower,includes the steps of closing the start-up blower system in-line valve;opening the or each isolation valve; and operating the or each blower tocirculate helium around the power generation circuit.